1. Field of the Invention
The present invention relates to the field of control of an internal-combustion engine, and more particularly control of a turbocharger system such an engine is provided with
2. Description of the Prior Art
Newly developed technologies for internal-combustion engines increasingly involve advanced engine control systems. In this context, new fluid system architectures require the development of new control strategies for the turbocharger system.
Control strategies for turbocharger systems based on static mapping with linear controllers are currently developed to control such a system. However, these strategies appear to be inadequate as they have the drawbacks as follows:                lack of robustness in relation to dispersions of the actuators and of the components,        great development effort: which on the one hand requires all of the static maps to be filled manually and on the other hand the regulator gains must vary depending on the operating point, and        interactions of the turbocharger system with the other engine sub-systems are not taken into account (therefore a change in the development of these sub-systems requires complete readjustment of the turbocharger regulator).        
Conventional strategies based on static mapping with proportional integral (PI) controllers are therefore inadequate. The introduction of control structures based on a model seems to be efficient and promising in order to meet this problem and to replace conventional linear controllers. In this context, several model-based approaches have already been provided in:                Schwarzmann, D., Nitsche, R., Lunze, J. “Diesel Boost Pressure Control Using Flatness-Based Internal Model Control”. SAE paper 2006-01-0855,        Stefanopoulo, A. G, Kolmanowsky, I., Freudenberg, J. S. “Control of Variable Geometry Turbocharged Diesel Engines for Reduced Emissions”. IEEE transactions on control systems technology, vol. 8 No. 4 July 2000.        
These strategies are based on models, that is physical, graphic or more generally mathematical representations of relations that really exist or that, by hypothesis, seem to exist between phenomena or between the various elements of the turbocharger system.
However, these models, described in the literature and intended to be used in a control law, involve two major drawbacks: on the one hand, they have too great complexity, which leads to adjustment problems, and on the other hand they do not take account of the dynamics. In fact, these conventional turbocharger regulation methods are based on mappings corresponding to static operating points. One then assumes that, in dynamics, the system goes through a succession of stationary (quasi-static) states.